1. Field of the Invention
The present invention relates to an image forming method for fixing a toner image in place on a recording medium with heat and pressure, which is applicable to electrophotographic image forming apparatuses such as copiers, printers, and facsimile machines.
2. Description of the Background
When toner particles adhering to the entire surface of a thin paper, from the leading end to the rear end, are fixed thereon in a fixing device of an electrophotographic printing apparatus, disadvantageously, the thin paper is likely to get jammed in the fixing device or wraparound a fixing member.
To prevent such paper jam or wraparound and facilitate separation of the paper from the fixing member, one proposed approach involves reducing the diameter of the fixing member to increase the curvature thereof. Another approach involves applying an oil to the fixing member to provide a release layer between the fixing member and toner particles. Further, another approach involves including a release agent (e.g., a wax) in toner particles.
As another approach, Japanese Patent Application Publication Nos. 2008-20821, 2005-284089, and 2001-265146 each disclose a fixing device including a fuser roller and a pressure roller each having 2 or more convex and concave portions in the axial direction. A fixing nip is defined by engaging the convex portions of the fuser roller and the concave portions of the pressure roller, and engaging the concave portions of the fuser roller and the convex portions of the pressure roller.
However, such a fixing device does not solve the problem of paper jam or paper wraparound when a recording medium is a thin paper or toner particles are adhering to the entire surface of the recording medium from the leading end to the rear end.
On the other hand, the above fixing devices do not have any problem in image gloss. Although the gloss of the first resulting image and that of succeeding resulting images may be slightly different due to decrease of the fuser roller temperature, the gloss is uniform throughout the entire resulting image because the entire surfaces of both the fuser and pressure rollers have a constant temperature.